Tectonics
Mohammad R. Ghassemi; Ali Aghanabti; Abdollah Saeidi
Abstract
Correlation of the orogenic and epeirogenic events in Iran with the events that have been identified in different parts of the world and in different tectonic environments, has caused some confusion in the Iranian geological literature. After a brief review of the nature of known orogenic processes in ...
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Correlation of the orogenic and epeirogenic events in Iran with the events that have been identified in different parts of the world and in different tectonic environments, has caused some confusion in the Iranian geological literature. After a brief review of the nature of known orogenic processes in the world, examining issues related to the abovementioned correlations, and considering the tectonic history of various parts of Iran, we have tried to systematically describe and name the important orogenic and epeirogenic events of the country. Most Precambrian orogenic events in Iran are dubious due to unknown age and poorly constrained tectonic setting of the rock units attributed to Precambrian. Paleozoic in Iran has been mostly associated with epeirogenic events, and the only sign of a real orogenic event goes back to the Late Carboniferous in northern Iran. The important Mesozoic and Cenozoic orogenic events have shaped the modern tectonic configuration of Iran. The Paleotethys suture in northern and central Iran formed during the Gorgani orogeny, development of the Central Iranian active margin (Sanandaj-Sirjan) occurred in the Ekbatani orogeny, ophiolite obduction in Central Iran and Zagros developed during the Late Cretaceous events, and collision of the Iranian plate with the Helmand block resulted in the Sistani orogeny. The creation of the Zagros and Alborz Mountain ranges started from Oligocene and Miocene times, respectively, and the deformation due to their shortening continues to this day.
M. Saadat; S. A. Alavi; A. Saeedi
Abstract
To analyze the paleostress in Sorkheh Hessar – Khodjir area, different shear – fault planes and the associated slickenside lineations are measured. The stress tensor and the variation of the stress direction in the upper Triassic to Oligocene formations are discussed. Numerous shear data ...
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To analyze the paleostress in Sorkheh Hessar – Khodjir area, different shear – fault planes and the associated slickenside lineations are measured. The stress tensor and the variation of the stress direction in the upper Triassic to Oligocene formations are discussed. Numerous shear data are determined from different locations in the study area and categorized into 16 sites according to the stratigraphic age. The main criteria used to identify the sense of slip are accretionary mineral steps, tectonic tool marks, polished and rough facets, and riedel shears. According to the inversion method which includes determination of the mean stress tensor orientation and sense of slip on numerous faults ,all data are classified based on tectonic events and the principal stress axes and corresponding compressional and extensional directions are calculated.
Based on the derived results from the diagrams, it is suggested that a prominent NE- SW compressional stress direction, which is obvious in Mesozoic and the younger Cenozoic formations, caused the deformation of the Mesozoic strata after Mesozoic and was continuous in Tertiary (Oligocene). It seems that a younger N-S stress direction exists and has had effects on both older and younger formations. It is believed that it would be related to one of the last Alpine orogenic phases.
